1. Field of the Invention
The present invention relates to an image processing apparatus for performing digital signal processing (for example, compression/expansion) on a color video signal.
2. Description of the Related Art
With the development of semiconductor techniques and image processing techniques, various image processing apparatus have been proposed and put into practice, such as an apparatus for recording and reproducing a television signal on and from a magnetic tape, a magnetic disk, an optical disk, a magneto-optical disk or other recording medium and an apparatus for transmitting a television signal to a remote place.
However, if the digital signal of a moving-image signal such as the television signal is to be transmitted (or recorded) without modification, a huge transmission capacity (recording capacity) and a high-speed processing circuit are needed. Accordingly, it is normal practice to compress the digital signal and transmit (record) the compressed digital signal and to expand the compressed digital signal on a receiving (reproducing) side. Typical examples of compression methods are subsampling and high-efficiency coding, and various other compression methods have been researched and proposed.
In normal practice, a luminance signal and color-difference signals which constitute a color video signal are processed by different processing lines because the luminance signal and the color-difference signals, if visually displayed, produce different effects on the visual sensation of human beings. For example, a digital video tape recorder (digital VTR) has been proposed which is arranged to apply intrafield processing to a luminance signal and interfield processing to color-difference signals. In this case, a deviation or a delay in time occurs between the luminance signal and the color-difference signals on a recording medium. In an expansion processing executed during reproduction, such deviation, i.e., a time delay, is cancelled or absorbed by delay means.
However, if the time delay is present between the signal components of the color video signal on the recording medium in the above-described manner, a reproduced image of a fast moving object will exhibit a deviation between luminance and chrominance even during normal reproduction. Also, if a single frame image is repeatedly reproduced as in the case of slow reproduction, a deviation between luminance and chrominance becomes distinct even if there is no fast motion in the reproduced image.